Change all null checking expressions to use 'is null' and 'is not null'
instead of '== null' and '!= null'.
This was mostly done with sed, so code can probably be improved in many
other ways with manual inspection, but that will come over time.
Also add code to the autoformat script to automatically fix these issues in the future.
This XM-only RemoveSelectors works on FieldDefinition but in some cases,
e.g. inside a generic types, it's FieldReference that are encoded. This
meant the static constructor was not re-written correctly and would throw
a TargetInvocationException (since the fields were removed correctly)
https://bugzilla.xamarin.com/show_bug.cgi?id=55693
Rolf Bjarne Kvinge
Sebastien Pouliot